This invention relates to subscriber terminals used with telephone lines and, in particular, to subscriber terminals requiring power to operate and to telephone lines requiring a continuous current for sealing the lines.
The newest types of subscriber telephone terminals, such as those containing microprocessors, require external power to function. Presently, these terminals obtain power via connection to the customer's standard electrical service. If for some reason this service is lost, the subscriber terminals cease to operate. Such loss of communication capability is particularly onerous in systems providing emergency phone service. Furthermore, in business related applications, the economic loss for lapses in communication capability can be substantial.
In systems of the described type, the subscriber terminals are served by tip and ring telephone lines which are brought to the subscriber's premises from the telephone central office. These lines must be kept free of corrosion. This is presently accomplished by a battery located at the central office.
Since the central office battery is continuously supplying sealing current, there is a likelihood that the battery may become drained. As a result, additional equipment must be provided at the central office for charging the battery. This adds to the cost and complexity of the central office which is undesirable.
It is an object of the present invention to provide an apparatus and method for supplying backup power for a subscriber terminal during power outages at the subscriber's location.
It is a further object of the present invention to provide an apparatus and method by which a continuous current can be generated for charging the central office battery without additional charging equipment at the central office.
It is still a further object of the present invention to provide an apparatus and method by which a required continuous sealing current can be provided on the tip and ring lines connected to a subscriber's premises even when the central office battery is low or drained.